This invention relates generally to dilatation catheters, and more specificially to over-the-wire dilatation catheters for angioplast.
Angioplasty is commonly carried out by use of a dilatation catheter which has an inflatable balloon at its distal end. The balloon catheter is typically guided through the patient's vascular system to a location adjacent the stenosis via use of a guide catheter. Then, using some imaging technique, e.g., fluoroscopy, the catheter is moved the remaining distance through the opening in the stenosis, i.e., "across" the stenosis. With the balloon within the stenosis, it is inflated by supplying a fluid, e.g., saline and a radio-opaque dye, whereupon the balloon's inflation stretches the artery and presses the lesion into the artery wall, thereby enabling increased blood flow through the artery.
Balloon angioplasty catheters are of two basic types, namely, the so-called "fixed-wire" type and so-called "over-the-wire" type. The fixed wire balloon catheter essentially comprises an expandable balloon fixedly secured onto a distal end portion of a guide wire. Such an instrument has a very narrow profile or "crossing size", i.e., a small cross-sectional area. Thus, the fixed-wire balloon catheter can easily cross its way through narrowed arteries so long as the tip or distal end can be negotiated through the artery. The major limitation with fixed-wire balloon catheters is the difficulty in steering the balloon wire tip into and through the narrowings or vascular restrictions. Another major limitation is that one balloon cannot be exchanged for another, e.g., a larger balloon, without first removing the first balloon. Such removal is undesirable since rethreading another fixed wire instrument to the vascular position of the first instrument vacated my not be possible or at the very least be difficult and potentially dangerous.
The over-the-wire balloon catheter essentially comprises an elongated catheter having a distal end portion at which an expandable balloon is fixedly secured and a central passageway through which a guide wire can be extended. With such an instrument a guide wire is first passed through the narrowed artery and then the balloon catheter is passed over the guide wire so that the guide wire is within the catheter's central passageway. While over-the-wire balloon catheters allow more flexibility in catheter placement and exchange, i.e., removal of one balloon catheter leaving the guide-wire in place so that a larger balloon catheter and be slid thereon to the vacated position, such catheters are not without their own limitations. In particular, a major limitation of over-the-wire balloon catheter instruments is that the tip crossing size is significantly larger than that of a fixed-wire instrument. Accordingly, the crossing of severely narrowed arteries with over-the-wire balloon catheters is made more difficult if not impossible.
Heretofore considerable efforts have been made to provide an over-the-wire dilatation catheter which is sufficiently flexible to pass through very tight tortuous paths, which exhibits good "pushability" (i.e., the transmission of longitudinal force along the catheter so that it can be readily pushed through the vascular system), and which has a reduced profile so that its balloon not only can reach but also can cross a very tight stenosis. Examples some prior art over-the-wire balloon catheters are found in U.S. Pat. No. 4,606,347 (Fogerty et al.), U.S. Pat. No. 4,863,440 (Chin), U.S. Pat. No. 4,932,959 (Horzewski et al.), U.S. Pat. No. 5,032,113 (Burns), U.S. Pat. No. 5,035,705 (Burns), U.S. Pat. No. 5,045,061 (Seifert et al.), U.S. Pat. No. 5,047,045 (Arney et al.) and U.S. Pat. No. 5,085,636 (Burns).
However, a need still presently exists for a balloon catheter which exhibits the small crossing size advantages of a fixed-wire instrument, with the positioning and exchange advantages of an over-the-wire instrument, all the while exhibiting good flexiblility and pushability.